Where winter temperatures annually drop to minus 5 degrees F, choose only winter-hardy grapes for the home vineyard. Average low temperatures of 0 degrees F are more easily tolerated. Since occasional bad winters do drop minimum temperatures below the normal range, give vulnerable grapevines extra care in their dormant season. Cold weather isn't the only threat, since winter drought could also stress the vines. Warm "false springs" during late winter could bring vines out of dormancy early, resulting in serious winter kill of fruiting canes when the winter chill returns.
Begin preparing new grapevines for winter by planting early. Planting vines in late winter gives root systems extra time to adjust. Late plantings produce new growth too late in the year to completely harden off for winter survival.
Prevent loss of grafted vines by burying the graft junction of the grape. Severe cold below minus 15 degrees F could kill vines back to the ground. Mounding dirt around the graft junction ensures that the graft and the rootstock survive. Pull the dirt back in spring before bud break.
Cut back on irrigation to grapevines in late August to trigger hardening off. During drought conditions recharge the soil in the vineyard with one thorough watering after the first frost, when vines are dormant.
Paint the trunks of grapevines with white latex paint in the early fall. White paint reflects winter sunlight and prevents grapes from breaking dormancy on warm winter days.
Postpone pruning until late winter. Prune out winter-killed wood before choosing which fruiting canes to keep and which to thin. Do only the rough work--cutting back large branch canes--and save thinning and trimming the fruiting canes until all danger of winter kill has passed.